Curable composition comprising cured filler, polymerized butadiene and di-alpha-cumyl peroxide and cured products thereof



United States Patent O 3,083,175 CURABLE CMPSITHON COMPRiSiNG CURE!) FLLER, POLYMERIZED BUTADHENE AND Dl-a- CUMYL PERXDE AND CURED PRDUCTS THERESE Moyer M. Saord, Schenectady, and Robert L. Myers, Baliston Lake, NSY., assignors to General Electric Company, a corporation of New York Filed Mar. 27, 1956, Ser. No. 574,332 2 Claims. (Ci. 269-45.5)

This invention relates to curable compositions comprising: 1) polymerized 1,3-butadiene (hereafter called polybutadiene), and (2) di--cumyl peroxide, and the cured products thereof. This invention also relates to a process which comprises curing polybutadiene with dia-cumyl peroxide.

The feaures of this invention desired to be protected herein are pointed out with particularity in the appended claims. The invention itself may best be understood by reference to the following description taken in conjunction with the accompanying drawing.

`In reference to the drawing, the FIGURE shown therein represents a comparison of the durometer hardness (Shore A) of both alkali metal polybutadiene (hereafter defined) and emulsion polybutadiene (hereafter defined) as a function of the time of cure with and without peroxides.

Heretofore, polybutadiene has been cured with sulfur to produce both soft and hard elastomers. However, sulfur-cured polybutadiene is unstable and decomposes at elevated temperatures. Attempts have been made to produce stable vpolybutadiene without using sulfur as a curing agent. Thus, U.S. Patent 1,901,04Mchmidt et al. describes a method of preparing hard polybutadiene free of sulfur by heating the polymer at high .temperature for long periods of time such as at 250400 C. or higher for about a day or longer in the absence of air.

ln Cotman, Industrial and Engineering Chemistry, 44, pp. 1421-1428 (1952), polybutadiene was treated with various peroxides, but even by using these peroxides, a long thermal hardening period of many days was required before a suitable hard product could be obtained.

We have now discovered that polybutadiene can be cured with di-a-cumyl peroxide within a very short period of time in the absence of sulfur to produce a heat stable polymer having good physical, chemical and electrical properties. it is quite surprising, and in no way could have been predicted, that di-a-cumyl peroxide would cure polybutadiene Within such a short period of time, such as, for example, -30 minutes with as little as l percent of di-a-cumyl peroxide, since other peroxides do not produce comparable materials within the same period of time. The significance of the invention is that for the first time Apolybutadiene has been cured by a short-cure method attractive to commercial production to yield a hard, stable product.

The di-a-cumyl peroxidecured polybutadiene will hereafter be referred to as cumyl-cured polybutadiene.

In general, the invention can be carried out by milling polybutadiene on differential rubber rolls (which .can advantageously be heated if desired) as dia-cumyl per- Oxide is added andintimatelyincorporated.into the polymer. The rolled sheet is then pressed lin a mold or other suitable curing device for a short period of time, for example 15-30 minutes at l150" C. The cumyl-cured polyrice butadiene so produced has the characteristics of hard rubber and is superior to polybutadiene cured for the same period of time with other peroxides.

1,3-butadiene can enter into a polymer chain by either a 1,2- or 1,4-mode of addition; the 1,2-mode of addition results in the following dangling vinyl structure CH2-oreom n (hereafter called 1,2-polybutadiene) whereas the 1,4 mode of addition results in the following structure:

(hereafter called 1,4-polybutadiene). Two types of catalysts are generally used to polymerize 1,3-butadiene, namely the free-radical and the alkali metal type catalysts. When LEX-butadiene is polymerized by free-radical type catalysts such as peroxides, persulfates, etc. 'in an aqueous emulsion system, a higher proportion of 1,4-polybutadiene results as compared to the product produced by the alkali metal type catalyst where a higher proportion of 1,2-polybutadiene is obtained. Using free-radical catalysts one obtains polybutadiene having less than 25% 1,2-polybutadiene.

Although both free-radical polymerized butadiene (also called emulsion polybutadiene) and alkali metal polymerized butadiene (also called alkali metal polybutadiene) can be cured with di--cumyl peroxide, the valkali metal polybutadiene can be cured to a much harder product within a surprisingly shorter period of time than that required for emulsion polybutadiene. This may be due to .the fact that alkali metal polymerized butadiene which contains larger amounts of dangling vinyl group 1,2-polybutadiene) cures more readily with di-a-cumyl peroxide to produce a harder polymer than the free radical cured butadiene which has its residual double vbonds buried in the chain of the 1,4-polybutadiene. Inorder to cure polybutadiene yto a Very hard polymer within a short period of time, it is necessary to use polybutadiene having a high percentage of the 1,2-type; i.e. over 30% and preferably Sti-100% l,2-polybutadiene.

Among the alkali metal type catalysts which have been used -ito :produce Ypolybutadiene having :high percentages of 1,2-polybutadiene are alkali metals and compounds containing alkali metals. Thus, metals such as lithium, sodium, potassium, rubidium, cesium, sodium-potassium alloys, and compoundsfof these metals such as phenyl isopropyl potassium, triphenyl methyl sodium, lithium butyl, amyl sodium and the `like compounds have been yused to effect such polymerization.

Where as free radical catalysts tend to produce larger amounts of 41,l1-polybutadiene, catalysts of the alkali metal type tend to increase the natio of the 1,2-polybut-adiene.

However, temperatureas ,well as catalysts affect-theftype of polymer formed; for example, polybutadiene produced by polymerizing 1,3=butadiene with sodium at `110 C. contains about 15% ofthe 'L2-polybutadiene whereas 100% of 1,2-type polymer is produced when 1,3-butadiene is polymerized with sodium at C. Although fthe ratio ofthe 1,2- to'the 1,4-polybutadienecan be determined b-y ozonization, Yprobably thernore accurate method of ydetermining',t1-iis ratio is'by the use of infra-red spectra.

Infra-red curves identifying .t -e different types of polymers are `found in Dogadlrin et al., Rubber Chemistry and Technology, 24, pp. 59l-596 (1951), Hampton, Anal. Chem. 2l, pp. 923-926 (1949); and Meyer, Ind Eng. Chem. 4l, pp. 1570-1577 (1949). An excellent description of polybutadiene polymers is found in Whitby, Synthetic Rubber, pp. 734-757, Wiley and Sons, NY. (1954), wherein are described methods of preparing polybutadiene falling within the scope of this invention.

Since molecular weight is related to viscosity, viscosity measurements are a convenient method of expressing the molecular weight. Although polybutadiene gums of a broad intrinsic viscosity range can be employed, we advantageously have employed polybuta-diene having an intrinsic viscosity of about 1.0 to 8.0 or higher. Optimum properties are obtained using polybutadiene having an intrinsic viscosity of 3.0 to 6.0.

inherent viscosity is determined by a Viscometer such as an Gstwald viscomcter on a 0.25 percent solution of polybutadiene in benzene. This value is calculated as the natural logarithm of the ratio of ow time of the solution to the ilow time of the solvent divided by the concentration in grams/ 100 ml. Intrinsic viscosity [1;] is obtained by exltrapolating the inherent viscosity vs. concentration curve to zeroV concentration.

The above described polybutadiene can be cured toV products of this invention with di-a-cumyl peroxide,

which peroxide can be prepared in the manner described in Karascn et al., Journal of Organic Chemistry, 15, pp. 753-762 (1950). The proportion of this unique peroxide to polybutadiene can be varied over Wide limits depending on the characteristics desired in the final product. Preferably, we employ the peroxide in amounts ranging lfrom .l to l0 percent or higher, based on weight of polymer. Optimum properties and curing time are obtained with about from 1 to 4 percent of peroxide based on weight of polymer.

In order that those skilled in the art may ybetter understand how the present invention may be practiced, the following examples are given by way of illustration and not by way of limitation. All parts are by weight.

EXAMPLE l A rubbery polymer was prepared from l,3`butadiene and nely divided sodium using the technique described in Marvel et al., 1. Poly-mer Science I, p. 275 (1946). The following procedure was employed: Into la clean, dry bottle was placed 0.1 g. of finely divided sodium dispersed in toluene. Thereafter, g. of 1,3-butadiene was charged as a liquid. A small Iamount of the butadiene was allowed to evaporate to displace any air remaining in the bottle. The bottles wereV capped, and rotated at C. for a period of 48 hours. The residual catalyst was deactivated by -adding 50 ml. of a 10% solution of absolute ethyl alcohol in benzene. The rubber was recovered by precipitation Ifrom a benzene solution by addition of ethyl alcohol until polymer no longer precipitated. To this precipitated product was added 0.1% of phenyl--napthyl-amine as an antioxidant, based on weight of polymer. This unwashed polymer had tan intrinsic viscosity of 6.0 when measured in benzene solution. By infra-red analysis this product contained iat least 60% of l,2-poly!butadiene.

The polybutadiene prepared in Example l was milled on differential rubber rolls as 3% yof various peroxides (based on weight of polybutadiene) were added thereto. The rolled sheets were then pressed in la mold forY 30 minutes at 150 C. Thereupon the product'was tested for tensile strength, percent elongation (both measured by ASTM procedure D-638-46T). The durometer hardness (Sh-ore A) was determined by a pointer forced into i the test specimen. A scale from 0-1100 units indicates the hardness, higher readings indicating harder products (ASTM D-676-47T). The results are given inV Table I.

Table l Tensile Percent Ex. Peroxide Strength Elongation Durometer (psi.)

Di-a-cumyl peroxide 636 95 Tort-butyl perb emanata.-. 62 100 45 Di-tert-butyl peroxide 28,0 100 55 5 Benzoyl peroxide 77 1,200 (l) 1 Only slight eure; porous.

From this .table it is evident that cumyl-cured polybutadiene subjected to a short cure is superior to polybutadiene cured with other peroxides. When the cured product prepared in the manner of Example 2 was heat aged in air at 200 C. for 500 hours, it darkened slightly. This same sample was then further heat aged in lair at 300 C. `for 500 hours,- and although the surface was crazed and blackened, the material was not electrically conducting; the resin below the surface was still in good condition. By avoiding contact with air, it is possible to avoid charring even at these or higher temperatures. It is quite unexpected that a hydrocarbon material would be so heat stable at these high temperatures.

Another advantage of the di-os-curnyl peroxide over other peroxides is that it can lbe milled into the poly'butadiene gum at elevated temperature such as at l30 C., at which temperature the other peroxides prematurely decom-pose. This higher temperature milling insures more homogeneous mixing particularly when the polybutadiene gum is very stiif. in addition, because of heat stability of the peroxide, uncured polybutadiene-di-a-cumyl peroxide compositions can be shipped in commerce without deleterious effects.

Polymer-peroxide compositions which are stable during the forming operations, such as calendering, extrusion, etc. are particularly desirable because ease of processing of polymers is of extreme importance in commercial operations. For example, it is essential that polymers be capable of being extruded at high speeds in a continuous curing operation. The composition, therefore, should iiow easily, have a smooth surface, and a minimum of nerve. Thus, plasticity is very important, particulai-ly in the wire industry. Since gums are more plastic at elevated than -at lower temperatures, it is highly desirable to have a gum-peroxide composition that can be extruded at elevated temperature at a fast rate without prematurely curing. Thus, polybutadiene-di--cumyl peroxide compositions can be extruded at those temperatures at which other peroxides would prematurely decompose.

ln addition to possessing the physical properties described above, the electrical properties of curnyl-cured poly/butadiene prepared in the manner of Example 2 were tested. A part of the uncured polybutadiene prepared in the manner of Example l was washed with water on differential rolls before curing while another sample of the same material was not washed. Where the sodiumtype catalyst is deactivated with water or alcohols and the products `are allowed to remain in the polymer, the product is called unwashed. Where the deactivated catalyst is removed by washing with water, the product is called Washed The results are given in Table Il.

Table II Polybutadiene T" C RF. e' e" AC p DC p Unwushed 25. 5 0. 002 2. 6 0. 005 1X 1013 3X 1013 Unwashed 90. 0 D. 002 2 5 0. 004 8X10l2 SXlG VVaShed.- 25. o 0. 001 2 4 0. 003 '.lXlOlz 7)(l0ls Vv'ashed 90. 0 0. 001 2. 4 0. 003 lXlOla 7)(1013 It is of interest to note that although most insulating materials exhibit increased losses -as the ltemperature rises, both Washed and unwashed cumyl-cured polybutadiene exhibit a uniformity of losses at both room and at elevated temperatures.

The tests used in Table II were carried out .according to the following ASTM measurements: power factor (P F.) D-l50-47T, dielectric constant (E) 'D-'150-47T, loss factor (6) D-l50-47T, alternating current resistivity (ACp) D-257-46, and direct current resistivity '(DC/) D-25746.

EXAMPLE 6 Emulsion polybutadiene was prepared -by adding 25 parts of liquid 1,3-butadiene -to a chilled solution of 1.25 parts of soap flakes (Ivory Flakes), 0.3 -part of potassium persulfate, and 0.5 part of dodecyl mercaptan in 45 parts of water. The reaction vessel was rotated continuously at 50 C. for 48 hours, then cooled to the temperature of ice-water, vented, and the contents added with stirring to a concentrated aqueous solution (at 0 C.) of sodium chloride. Thereupon 200 cc. of a 2% H2804 solution was added =to the slurry. After the product was -freed of `acid and salts by Water Washings, water was removed by washing with alcohol and placing Vthe resulting product in a desiccator for 48 hours to remove .the residual alcohol. An antioxidant (phenyl--naphthylamine 0.1% based on polymer) was then milled into the product.

In addition tothe method described in Example Y6, emulsion polymerized polybutadiene can be prepared by other methods known to the art as for example those methods disclosed in Whitby, Synthetic Rubber, John Wiley & Sons (1954), pp. 699-701.

The durometer hardness (Shore A) of both alkali metal polybutadiene and emulsion polybutadiene cured by various methods were compared. These results are shown in the drawing wherein -durometer hardness is plotted against time of cure (on a logarithmic scale), The unbroken line curves refer to sodium polybutadiene, while the broken line curve refers to emulsion polybutadiene. Curve A represents sodium polybut-adiene (prepared by the method of Example 1) cured without peroxides at 150 C.; curve B represents sodium polybutadiene (prepared by the methodof Example 1) cured without peroxides at 200 C.; curve C represents emulsion polybuttadiene (prepared according to the method of Example 6) containing 1% di-a-cumyl peroxide, based on weight of polymer, cured at 150 C.; curve D represents sodium polybutadiene containing 1% Id i-nL-cumyl peroxide cured at 150 C.; and curve E represents the same composition as curve D at 170 C. From this graph it 'is evident that the cure without peroxides is extremely slow; that emulsion polybutadiene does not cure to a very hard product as readily as does the alkali metal polymer; and that with di-.a-cumyl peroxide a faster cure is eiected at 170 C. than at 150 C.

A problem which is encountered in curing polybutadiene is that of shrinkage. Thus, when `polybutadiene is cured with either heat or peroxides, a shrinkage of over 4% is noted. Although this ydoes not Vaect many uses to which polybutadiene is applied, it is somewhat objectionable in molding applications,

We Ahave found that this defect can be corrected by incorporating organic or inorganic fillers into the polyb-uta.- diene-di-a-cumyl peroxide composition and curing the filled product. In addition, these -cured filled products are less brittle than the cured, unfilled polymer.

Among the fillers that can be employed are various types of carbon blacks, silicas, aluminas, and calcium silicate as disclosed in application Serial No. 509,387-Precopio et al., tiled May 18, 195,5, and assigned to the same assignee as the present application; silicas rendered hydrophobic by surface treatment Iwith: (l) alcohols in the manner described in U.S. Patent 2,657,149-ller, and (2) with trialkylsilanes in the manner of Bueche et al., appli- 6 cation Serial No. 531,829, vtiled August 31, 1955, and assigned to the ksame assignee as the present invention. Other llers can also be used, such as, for example, titanium dioxide, zinc sulfide, `calcium carbonate, zinc oxide, magnesia, clays, etc.

In addition to inorganic fillers, such as those described above, organic fillers can also be used. Organic iillers have the advantage -as they are capable of reducing shrinkage and brittleness without appreciably affecting electrical properties. Among organic fillers are: coumarone-indene resins, petroleum resins, polyterpene lresins (such as those described in Modern Plastic Encyclopedia, 1955, pp. 82-84), high styrene resins, such as high styrene-low butadiene copolymers, -lignins, w-ood flour, styrene-isobutylene resins, phenolic resins, etc.

We have unexpectedly found that if cumyl-cured polybutadiene is ground into a tine powder and then compounded as a filler in uncured polybutadiene, and subsequently cured With di-a-cumyl peroxide, shrinkage was reduced to less than 1/2% Without harming vthe physical or electrical properties as will be shown in the following example.

EXAMPLE 7 Cumyl-cured polybutadiene prepared by the method of Example 2 was tinely ground. Forty parts of this powder were incorporated into parts of polybutadiene prepared in Example l and milled on differential rubber rolls as 3% of di-a-cumyl peroxide was Iadded. The rolled sheet was then pressed in a mold for Q10-minutes at 150 C. When the cured product -was removed from the mold, it was noted that less than 1/2% shrinkage had occurred. The physical and electrical properties were compared to cured polybutadiene prepared inthe manner of Example 2 and found to be substantially identical.

EXAMPLE 8 Forty parts of wood iiour were milled into 100 parts of the polybutadiene prepared in Example l as 3% of di-a-cumyl peroxide was added. The rolled sheets were then pressed in a mold for 30 minutes at 150 C. When the cured product was removed from the mold, it was noted that less than 1/2% shrinkage had occurred. This product Awas also less brittle than polybutadiene prepared vby the Amethod of Example 2.

By using di-a-cumyl peroxide, -polybutadiene can be cured within a short time to a heat stable material possessing .good chemical, physical, and electrical properties. The `product is insoluble in the common solvents and is very hard. It is surprisingly inert to most chemical 'agents and does not soften or decompose at very high temperatures. Since its electrical conductivity is very low, it makes lan excellent insulating material. Because it can be prepared as a colorless, transparent or -translucent material, it has excellent eye appeal.

Polybutadiene can be used to prepare molded, calendered or extruded articles, lfilms, coatings, threads, or filaments, tapes `and .the like. The cumyl-cured molded, calendered or extruded articles possess extreme Lhardness yet possess suiiicient elasticity to be applied to a broad spectrum of uses, such as sheets, rods, tubes, etc. useful in electrical applications, such as cable terminals, terminal blocks, backing for electrical circuits, Vas components of dynamoelectric machines that operate -at high temperature, etc. Films of this materialcan be prepared by dissolving or suspending the uncured polybutadiene-peroxide composition in a suitable solvent, such as cyclohex-ane, chlorinated solvents, such as methylene chloride, ete. fol lowed by spreading and curing on a surface from which the ,polymer can be removed after drying. As a kcoating material, the uncured polybutadiene-peroxide composition can be applied as a solution or suspension to any convenient foundation where a hard, durable, scratch resistant surface is desired, yand subsequently cured. It can be used as an encapsulation material for insulation, for example,

as a wire enamel, etc. ln a solution or suspension the uncured composition can be extruded into air which has been heated to suciently high temperature to cure the polymer and to drive oil the solvent. The fibers so produced can be woven in fabrics that can be used as iilter cloths where high chemical and heat resistance is desired.

Cumyl-cured polybutadiene can also be used in many everyday articles where extreme hardness is needed, for example, as doorlinobs, cigarette holders, buttons, pen holders, combs, casings for portable radios and television receivers, and other articles which are subjected to hard use.

The products of this invention can also be used as laminates, i.e. products made by bonding together two or more layers of materials. These laminates may contain iler materials, such as ground quartz, etc. and may be prepared by impregnating a material, such as paper, glass, cloth, sheets of metal, other resins, etc. Because of their superior properties, laminates of polybutadiene can be used as table or counter tops, sink tops, work benches, wall panels, baseboards, wainscoating, elevator linings, and many other applications which require hard, durable materials, such as the interior iinishing of public places, for example, the interior parts of hotels, passenger transportation equipment, etc` lts excellent electrical properties malte laminates of this material useful for electrical equipment, such as slot wedges in the armature of an electric motor, panel boards for printed circuits, electrical appliance panels, radio and television panels, small punched electrical pieces, transformer terminal boards, switchboard panels, transformer coil spacers, etc.

Polybutadiene can also be compounded with an abrasive material (such as sand, Carborundum, alumina, tungsten carbide, diamond dust, and other abrasive materials) and cured with di-oc-cumyl peroxide according to this invention. Polybutadiene acts as an excellent binder for abrasives since it is tough, adhesive, resist-ant to heat, etc. Abrasive wheels can be prepared by sandwiching polybutadiene loaded with abrasive between glass cloth, pressing, and curing. In preparing abrasive materials (although the Kamount of polybutadiene will vary with the particular abrasive), it is advantageous to use as little polybutadiene as possible consistent with proper binding of the abrasive, i.e. 50% or more of the abrasive material based on total weight.

EXAMPLE 9 Blocks of abrasive materials are prepared by milling 1() parts of polybutadiene (prepared by the method of Example 1), 0.3 part of di-a-cumyl peroxide and 60 parts of the following abrasives: (l) Carborundum, (2) alumina, (3) tungsten carbide, (4) sand, and curing the milled material. Hard, cohesive blocks of abrasive materials are produced which are capable of sharpening implements, such as knives, etc.

In addition, the compositions of this invention can be used as potting gels for electrical insulation, for example, in motors, transformers, etc. in general these potting gels are prepared by (1) dissolving polybutadiene in a liquid potting medi-um of good electrical properties such as hydrocarbon oils, low molecular weight polyisobutylene, organic polyesters, etc., (2) adding dicumyl peroxide thereto, (3) pouring this composition into the area to be insulated, (4) heating so as to gel this composition.

The electrical insulating properties of these potting gels are excellent. Dicumyl peroxide is an excellent peroxide to use as 'a curing agent since unlike most peroxides it gives ott no acids on decomposing. Although the amount of polybutadiene and dicumyl peroxide in the potting 8 composition can be varied within wide limits, we have advantageously employed 5-15% of poli/butadiene, and from 15% of dicumyl peroxide, based on total composition.

EXAMPLE 10 A potting gel was prepared by dissolving 10 parts of lsodium polybutadiene (Example 1) in 90 parts of a highly refined hydrocarbon oil used in transformers (viscosity 10 centistokes) by heating the mixture to 125 C. This composition was then cooled to about C. and 1 part of dicumyl peroxide was added thereto. This composition was then poured into the section o a motor to be electrically insulated, where it was cured by heating for 30 hours-at about 15G-160 C. The product, .a soit gel, exhibited excellent electrical properties.

Firmer gels were prepared by varying the amount of dioumyl peroxide. For example, we repeated the above procedure except that 2 and 4% of dicumyl peroxide was employed in place of 1% peroxide to produce a irmer gel.

The hardness of the product can be varied by using varying amounts of peroxide. It is often desirable to 1add antioxidants, for example, phenyl--naphthyl amine, the reaction product of diphenyl amine and acetone, tri- `phenyl phosphite, Vdi-tert-.butylhydroquinone, alltylated phenols and the like to the product. When antioxidants Aare used, larger amounts of peroxide are generally required to effect a satisfactory cure. In addition, plasticizers, e.g. hydrocarbons, metal salts of fatty acids, aliphatic and aromatic esters, polyorganosiloxane oils and gums, etc. can Ialso be incorporated into the curable mixture. By varying the kinds of these auxiliary materials, it is possible to vary the properties of the product within wide limits. Dyes, pigments, and the like can also be added to produce a resin in the desired color.

What we claim as new and desire to secure by Letters Patent ofthe United States is:

1. A curable composition which exhibits little shrinkage on curing, which comprises (1)49. filler which is finely ground, cured, alkali metal polymerized 1,3-butadiene wherein the polymerized 1,3-butadiene comprises at least 30% 1,2-polybutadiene, said finely ground iiller being cured with di-rx-cumyl peroxide, (2) alkali metal polymerized 1,3-butadiene comprising at least 30% 1,2- polybutadiene, and (3) 0.110% di--cumyl peroxide based on the weight of the polymerized 1,3-butadiene.

2. The cured product of claim 1.

References Cited in the iile of this patent UNITED STATES PATENTS 2,422,153 Van Nimwegen et al. lune 10, 1947 2,558,527 Rumscheidt et al lune 26, 1951 2,676,944 Doak Apr. 27, 1954 2,690,461 Steeves Sept. 28, 1954 v 2,819,255 Boardman Jan. 7, 1958 2,819,256 Boardmi Jan. 7, 1958 2,835,642 Salford et al May 20, 1958 OTHER REFERENCES Warden: India Rubber World, volume lli of 1944, pages 309 to 311, 260-773.

Whitby: Synthetic Rubber, published by lohn Wiley and Sons, New York 1954, pages 734 to 757.

Chemical and Engineering News, vol. 33, No. 20, page 2079, May 16, 1955.

Braden et al.: Transactions oi' the Institution of the Rubber Industry, volume 3l, No. 6, part il, December 1955, pages to 165. A 

1. A CURABLE COMPOSITION WHICH EXHIBITS LITTLE SHRINKAGE ON CURING, WHICH COMPRISES (1) A FILLER WHICH IS FINELY GROUND, CURED ALKALI METAL POLYMERIZED 1,3-BYTADIENE WHEREUB THE POLYMERIZED 1,3-BUTADIENE COMPRISES AT LEAST 30% 1,2-POLYBUTADIENE, SAID FINELY GROUND FILLER BEING CURED WITH DI-A-CUMYL PEROXIDE, (2) ALKALI METAL POLYMERIZED 1,3-BUTADIENE COMPRISING AT LEAST 30% 1,2POLYBUTADIENE, AND (3) 0.1-10% DI-A-CUMYL PEROXIDE BASED ON THE WEIGHT OF THE POLYMERIZED 1,3-BUTADIENE. 